1. Field
The present disclosure relates to a control method of a differential pressure water electrolysis system.
2. Description of the Related Art
Generally, hydrogen is used as a fuel gas employed in power generating reaction in fuel cells. Hydrogen is produced by a water electrolysis device, for example. Water electrolysis devices use a solid polymer electrolyte membrane (ion-exchange membrane) to perform electrolysis of water and generate hydrogen (as well as oxygen). Both sides of a solid polymer electrolyte membrane are formed of an electrode catalyst, forming an electrolyte membrane-electrode structure. Feed conductors are provided to either side of the electrolyte membrane-electrode structure, making up a unit cell.
Multiple unit cells are laminated to form a cell unit. Voltage is applied to both ends of the cell unit in the laminar direction, and water is supplied to the anode side feed conductor. Accordingly, water electrolysis was performed at the anode side of the electrolyte membrane-electrode structure, by which hydrogen ions (protons) are generated, the hydrogen ions transmit through the solid polymer electrolyte membrane and migrate to the cathode side and bind to electrons, thereby producing hydrogen.
Hydrogen derived from a cell unit is sent to a gas-liquid separator where liquid water is removed, and then supplied to a hydrogen purification unit, thereby yielding the product hydrogen (dry hydrogen). On the other hand, at the anode side, the oxygen generated together with the hydrogen is discharged from the cell unit along with excess water.
A differential pressure water electrolysis device (high-pressure hydrogen production device) is a type of water hydrolysis device where oxygen is generated at ambient pressure at the anode side, while high-pressure (generally 1 MPa or higher) hydrogen is generated at the cathode side. The differential pressure water electrolysis device at this time has high-pressure hydrogen filled in a channel of a cathode-side separator, and ambient-pressure water and oxygen in a channel of an anode-side separator, across the solid polymer membrane. Thus, when stopping operation (ending supply of generated hydrogen), hydrogen remaining at the cathode side may cross-leak to the anode side, so the pressure difference on the two sides of the solid polymer membrane needs to be removed to protect the solid polymer membrane.
Japanese Unexamined Patent Application Publication No. 2010-236089 discloses a method of stopping operation of a water electrolysis device. This operation stopping method includes a process to apply voltage after supply of oxygen from the cathode side has been stopped, and a process to depressurize (release pressure) at the cathode side at least, with the voltage applied. According to this arrangement, if hydrogen at the cathode side leaks to the anode side, the hydrogen becomes protons again due to the applied voltage, transmits the electrolyte membrane by the hydrogen film pump effect and return to the cathode side.
Accordingly, retention of high-pressure hydrogen which has leaked to the anode side can be suppressed after ending operation, thereby preventing reduction (deterioration) of the catalyst electrodes by the hydrogen.